SEATTLE – These machines are scattered across the country, designed to keep you safe. But are they?

Now, some researchers are sounding the alarm about airport scanners and the radiation they give off. This new research is fueling a backlash against the new system, which could roll out in Portland International Airport as early as 2011, that already has at least one privacy group suing over civilian privacy rights and flight attendants calling for a "pat-down opt-out day" Nov. 24.

"If you think of the entire population of, shall we say, a billion people per year going through these scanners, it's very likely that some number of those will develop cancer from the radiation from these scanners," said David Brenner, director of the Center for Radiological Research at Columbia University and a professor of radiation biophysics.

Brenner told CNN that while the risk of harmful radiation exposure from what is known as "backscatter" scans is very small, he is concerned about how widely the scanners will be used.

"I just checked today ... [through] the end of December of this year, and Portland is not on" TSA's deployment list, said Dwayne Baird, spokesman for the TSA Northwest Region. "And they have not released the deployment schedule for next year."

As a result, Baird said he also doesn't yet know whether PDX is in line to receive the backscatter machines or another "Advanced Imaging Technology" option.

Scanner safety
To be sure, security experts say the use of full-body scans may have prevented the Christmas 2009 "Underwear Bomb" attempt to blow up a Northwest Airlines flight. That's because scanners, which can cost six figures each, screen airline passengers without physical contact and can reveal plastic or chemical explosives and non-metallic weapons.

Two major pilots' unions have already spoken out against airport rollout of scanning machines with backscatter X-ray technology. These backscatters scans are used at Sea-Tac and some other airports. A second type – millimeter-wave machines – are used at the remaining airports across the U.S.

The TSA maintains the machines are safe, and that they've been evaluated by the Food and Drug Administration's Center for Devices and Radiological Health, among other agencies. The total number of imaging machines is expected to near 1,000 by the end of 2011, according to the Transportation Security Administration.

"TSA sets strict standards for all of its technology to include detection capabilities, operational capabilities and health and safety standards," the agency said in a statement. "The two approved technologies that meet all of those standards are backscatter and millimeter wave."

Apprehension mounts
Still, a number of airline pilots share apprehension over the repeated use of the scanners.

"The cumulative effect of additional radiation exposure on top of what we do flying the aircraft, over a 10- or 20- or 30-year career, begins to mount up," said Dave Bates, president of the Allied Pilots Association.

The APA joined the US Airline Pilots Association this week in urging union members not to submit to body scanners at airport security checkpoints. The unions, collectively, have around 16,000 members.

Some passengers at Sea-Tac shared a similar worry.

"That would definitely be a concern. I wouldn't want extra exposure without good reason," said Wendy Valdez of Yakima.

"The radiation is more important to me than the security is good," added Joyce Albers, a part-time Seattle resident.

"[I'd] probably want to know more about it, but there's a lot of things we have in life that give off a lot of radiation we don't know about," wondered Peter Abler, a traveler from Los Angeles.

In April, a team of researchers from the University of California, San Francisco, sent a letter to the government urging for independent studies to be done.

"The dose to the skin may be dangerously high," wrote a team of scientists, adding that there could be risks to certain population segments, including children, senior citizens and women susceptible to breast cancer.

Support of backscatter technology
Among those supporting backscatter technology is The American College of Radiology, a group of more than 34,000 professionals including radiologists, oncologists and medical physicists.

"The ACR is not aware of any evidence that either of the scanning technologies that the TSA is considering would present significant biological effects for passengers screened," the organization said in a statement.

The group added that passengers would have to undergo about 1,000 scans in one year to reach the same amount of radiation as a regular chest X-ray.

Passengers have the choice to opt out of the body scanners. Those who do will instead receive additional screening, including what the TSA describes as an enhanced pat-down. Those enhanced pat-downs went into effect at all airports nationwide, including the Portland International Airport, on Oct. 29. Passengers also can request a private screening, where all belongings are taken to the private screening area with all secondary inspections completed there.

As an aside, in 2006 PDX installed machines to hit passengers with quick bursts of air. That air was used to dislodge small particles, instantly analyzed for traces of explosives. However, those machines were removed from the airport in 2009.